Due to license issues Ubuntu will no longer distribute Oracle's JDK and JRE. Also previous versions supplied on PPAs suffer from security issues are are not recommended to be installed on any Ubuntu system.

There are no more supported java releases from Ubuntu - Ubuntu officially supports OpenJDK and OpenJRE implementation of Java which is the base for Oracle's own implementation.

To install the OpenJDK & OpenJRE refer to this Q&A.

The instructions below provide a guide to install the official Oracle JDK 6. You will need to regularly update this manually to ensure your installation maintains recommended security and stability fixes.

Install the Oracle JDK 6

Oracle JDK 6 is no longer maintained. It is not updated with the latest security patches and are not recommended for use in production.
You can however still download them from the Oracle Java Archive

Oracle themselves have the official guide to install their JDK - below is based upon those instructions.

• Download the 32bit or 64bit Linux "compressed binary file" - it has a ".bin" file extension

• Give it permissions to execute and extract it

  chmod a+x [version]-linux-i586.bin

  ./[version]-linux-i586.bin

During installation it will ask you to register - press ENTER. Firefox will open with the registration page. Registration is optional.

JDK 6 package is extracted into ./jdk1.6.0_x directory, for example ./jdk1.6.0_30.

Lets rename it:

mv jdk1.6.0_30 java-6-oracle

• Now move the JDK 6 directory to /usr/lib

sudo mkdir /usr/lib/jvm

sudo mv java-6-oracle /usr/lib/jvm

switch to Oracle JDK 6

webupd8.googlecode.com hosts a nice-easy script to help with this.

wget https://storage.googleapis.com/google-code-archive-downloads/v2/code.google.com/webupd8/update-java-0.5b
chmod +x update-java-0.5b
sudo ./update-java-0.5b

don't worry - 0.5b refers to the script version - not the version of java!

An alternative to this is to use the webupd8 ppa and the update-java package.

Finally test the switch has been successful:

java -version
javac -version

These should display the oracle version installed - 1.6.0_30

Install the Firefox/Chrome plugin

In a terminal:

mkdir ~/.mozilla/plugins

Remove the IcedTea plugin, if it has been installed.

sudo apt-get remove icedtea6-plugin

Remove a former version of the Java plugin (may or may not be present)

rm ~/.mozilla/plugins/libnpjp2.so

Now you can install the plugin, by creating a symbolic link (you tell Firefox, where the plugin is located).

(32bit)

ln -s /usr/lib/jvm/java-6-oracle/jre/lib/i386/libnpjp2.so ~/.mozilla/plugins/

(64bit)

ln -s /usr/lib/jvm/java-6-oracle/jre/lib/amd64/libnpjp2.so ~/.mozilla/plugins/

Confirm that the JRE has been successful by using the official oracle website.

Linked Questions:

1. How do I install Java?
2. How do I install Oracle Java JDK 7?
3. How can I install Sun/Oracle's proprietary Java JDK 6/7/8 or JRE?